Do this: https://pve.proxmox.com/wiki/Upgrade_from_8_to_9 No need to overthink it too much. I've done several so far.

Run the pve8to9 script first to do some sanity checks (it should already be installed if the system is up to date).

Update the box to latest 8.x with apt update etc. Change the package sources to the new ones and update the system.

The packages databases can be a bit confusing: You have two lots - stock Debian and Proxmox (enterprise OR no-subscription).

Stock Debian is in the single file /etc/apt/sources.list - change "bookworm" to "trixie".

Proxmox sources is in a file in /etc/apt/sources.list.d/ Remove all of the Proxmox related ones you have there and run this (or do it yourself with an editor). This example is no-sub - the official doc notes the enterprise equivalent:

  cat > /etc/apt/sources.list.d/proxmox.sources << EOF
  Types: deb
  URIs: http://download.proxmox.com/debian/pve
  Suites: trixie
  Components: pve-no-subscription
  Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
  EOF

Run apt dist-upgrade then the pve8to9 script again and then reboot. If in doubt choose Y for install the maintainer's version when prompted. There are notes in the doc about several packages.

Job done.

▲ snailmailman 2 hours ago | parent [-]

I just followed their guide last week and was surprised how smooth it went. Their documentation seemed very thorough. I kinda expected a few issues, but everything worked flawlessly. Seems like they do a pretty good job of detecting most of the edge cases that would cause issues. Granted, my installation hasn’t been modified too heavily outside the norm. I think I had one or two modified config files I had to edit, but the helper script found and told me about them and how to handle it.

I had put off the upgrade for a while figuring it would be a breaking change. But it went so smoothly I’ll probably be upgrading to 9.1 pretty soon.

	▲	gerdesj 2 hours ago \| parent [-]
		Quite. Its almost as though the docs are written by people who actually use it. I was (still am sadly) a VMware consultant for about 25 years. It makes me laugh when I hear breathless "enterprise noises" with regards VMware and how PVE isn't quite ready yet. PVE is just so easy and accommodating. It's Linux on Debian with a few nobs on. The web interface is so quick and uncluttered and simple. The clustering arrangements are superb and simple. The biggest issue for me and many like me was how to deal with iSCSI SANS (no snapshots - long story) It turns out you can pull the SSDs out of a Dell Msomething SAN and wack them into the hosts and you have a hyperconverged Ceph thingie with little effort. VMware rapidly gets very expensive. Nowadays with Broadcom you have to fork out for the full enterprise thing to get DRS and vDS - that's auto balancing clusters and funky networking. PVE gifts you Open vSwitch support out of the box and all clusters are equal. Storage DRS (migrate virty hard discs on the fly) is free on PVE too. Oh and you get containers too on PVE - VMware Tanzu is seriously expensive. Anyway, I could grind on about this for quite some time but in my opinion, PVE is a far better base product in general for your VMs. A vCentre is a horrendous waste of resources and the rest of VMware's appliances are pretty tubby too. I recall evaluating their first efforts at SDN with edge firewalls and so on - no thanks!